This invention relates to a new wind driven turbine with improved efficiency to generate electric power, and in particular to a turbine design that augments the fluid stream towards the blades of the turbine. The present invention relates broadly to apparatus for increasing the flow speed of a fluid medium such as air or water and for recovering its kinetic energy. This invention further relates to the harnessing of wind power for converting kinetic wind energy to mechanical and/or electrical power. The present invention is described with reference to wind as the medium; however, those of ordinary skill in the art will appreciate that the invention is applicable to other fluid mediums (e.g., gases and liquids), such as steam and water.
Because energy from the wind is free and non-polluting, much affention has been given to improving the efficiency and lowering the cost of windmill structures. Energy has been extracted from moving air for thousands of years using hundreds of different designs from the simplest sails that push ships to sophisticated computer controlled windmills that generate electricity. After many hundreds of years of refinement, the basic three bladed (propeller type) windmill design using computer controlled variable pitch airfoils has become the dominant means for generating electricity. All of these different solutions take advantage of the principle that the faster the relative wind, then the more energy that can be extracted. An efficient three bladed windmill extracts about one-half of the kinetic energy in the wind to spin the blades. However, there are some limitations with that conventional design approach. For example, the speeding blade tips can shed vortices and create swirl wakes that steal energy while the shaft end of the blade next to the center hub hardly moves. Using twisted (variable pitch) blades help accommodate the rotational speed difference between the hub and the blade tip, but it cannot perform with optimal output for the full dynamic range of the fluctuating winds.
It is well known that the recoverable kinetic energy is proportional to the third power of the wind velocity or speed. Thus, doubling the air speed will increase the power recovered by eight times. However, there are generally acknowledged minimum wind speeds that will result in recoverable energy. It is generally acknowledged that a wind speed of five meters per second or about eleven miles per hour is required in order to make energy recovery economically feasible. In many areas of the world, the predominant wind speed is at or only slightly above the level required for economical energy recovery and, therefore, wind energy has not been harnessed effectively. It is important to note that the total kilowatt hours produced over a period of time with a wide range of wind velocities is more important than how many kilowatt-hours the windmill can produce at its maximum design speed. How much power it produces when the prevailing wind is just a breeze or when it is the strongest of winds are important factors in the total equation.
The amount of power that a conventional propeller windmill can generate is directly proportional to the square of the diameter of the circle of rotation of the propeller tips, as well as the cube of the wind velocity. It is also known that the further from the axis of rotation the wind force can be applied, the greater the generated torque or rotational force. Further, increasing the diameter of the propeller decreases the rotational speed of the windmill. The longer blades are more difficult and costly to make so they must be light in weight, properly shaped and capable of responding to the prevailing wind without undergoing excessive deflection, distortion or failure.
Some horizontal axis windmill designs investigated incorporate a funnel that employs the Principle of Continuity that states that the product of the velocity and the cross sectional of an air-stream area remains constant. Accordingly, the velocity in an air stream must increase when passing through such constrictions. For example, if the exit area in a funnel were one-half of the entrance opening, then the air would have to exit at double the intake velocity, providing a so-called Venturi effect. However, such known designs have the disadvantage that most of the oncoming air does not enter the funnel but would flow around the outside due to backpressure. Further, the small amount of air that does pass through the funnel would be directed at the central area around the hub of the windmill where it would be least effective in generating power. Others claim a more efficient design using the Venturi principle by proportioning an exterior truncated cone or collector fin to capture more of the air and by adding an inverted cone or stream liner in the center of the cone to divert the air out and around a central generator and into a series of turbine blades. The following patents are related to windmills and turbines, the contents of each are hereby incorporated herein by reference: U.S. Pat. Nos. 4,140,433; 4,320,304; 4,411,588; 5,457,346; 6,382,904.
Basically, Venturi based windmill inventions first capture some wind, and then try to squeeze and accelerate it through one or more cone shapes in front of the turbine blades. No prior known wind turbine systems have utilized the approach of first accelerating the wind in a laminar flow around a streamlined body before it captures the accelerated air and sends it through the circumferentially mounted turbine blades. The accelerated “laminar air” that flows over an aircraft wing to help lift it up into the sky contains the same kinetic energy stream used by the turbine of the present invention to generate electricity.
There is a need in the windmill and turbine art for a wind driven power generator that is capable of generating substantially more power than equal diameter conventional propeller windmills. There is a further need for a wind driven power generator that is compact in size, including several discrete subassemblies that can be made with a modular construction, and is adapted to incorporate and drive an electrical power generator and/or an apparatus for driving an external electrical power generator or other device.